libswscale/x86/hscale_fast_bilinear_simd.c: Include BX in the clobber list on x86_64, because it isn't implicitly included when PIC is on.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 48e9f68384)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/x86/hscale_fast_bilinear_simd.c

@@ -277,7 +277,7 @@ void ff_hyscale_fast_mmxext(SwsContext *c, int16_t *dst,
           ,"m"(retsave)
 #endif
         : "%"REG_a, "%"REG_c, "%"REG_d, "%"REG_S, "%"REG_D
-#if !defined(PIC)
+#if ARCH_X86_64 || !defined(PIC)
          ,"%"REG_b
 #endif
     );
@@ -361,7 +361,7 @@ void ff_hcscale_fast_mmxext(SwsContext *c, int16_t *dst1, int16_t *dst2,
           ,"m"(retsave)
 #endif
         : "%"REG_a, "%"REG_c, "%"REG_d, "%"REG_S, "%"REG_D
-#if !defined(PIC)
+#if ARCH_X86_64 || !defined(PIC)
          ,"%"REG_b
 #endif
     );